Statistical contention is rapidly becoming a preferred technique for controlling local area communication networks and the like. The basic statistical contention network control process is described in a commonly assigned Metcalfe et al. U.S. Pat. No. 4,063,220, which issued Dec. 13, 1977 on a "Multipoint Data Communication System with Collision Detection". Moreover, that process is now in use, for example, in connection with the Xerox Ethernet local area network.
As is known, statistical contention control (1) gives each terminal on a communications network equal access to a shared communication medium on a contention basis and (2) resolves any "collisions" that occur when two or more terminals more or less simultaneously attempt to transmit over the communications medium by resetting those terminals to retry at randomly selected later times. In packet-type communication networks, such as the Ethernet local area network, collisions are relatively rare, and the delays that are encountered when collisions do occur are usually so brief that they are generally imperceptible to the ordinary user.
Reliable collision detection is, of course, essential for successful statistical contention network control. Heretofore, in keeping with the teachings of the aforementioned Metcalfe et al. patent, the collision detection function has been performed at the transceivers which interface the terminals to the comunications medium. That has proven to be a completely acceptable response to the collision detection requirement for networks employing coaxial cable as the communications medium, such as the Ethernet network. However, efforts to embody the collision detection function in the transceivers for the terminals of optical communications networks have led to the conclusion that such an embodiment requires that the transceivers either have DC coupled receiver sections or be equipped with relatively complex and expensive timing circuitry. As a result, designers of such transceivers have been faced with difficult cost/performance tradeoffs.